Slow Photon Effect Research Articles

Plasmonic-3D photonic crystals microchip for surface enhanced Raman spectroscopy

Plasmonic-dielectic hybrid substrates of Ag-islands on three-dimensional photonic crystals are fabricated through magnetron sputtering of silver onto hydrophobized silica photonic crystals, free from etching process. Without typical “hot-spots” such as nanogaps, significant Raman enhancements can be achieved, attributed to the enhanced electromagnetic field and scattering of the plasmonic nanoparticles as well as the enhanced light-matter interaction by the slow photon effects. The detection limit for adenine by the hybrid substrates reaches nM level, with a calculated enhancement factor of 1.13 × 107, which is three orders of magnitude higher than the conventional noble metal film over nanosphere (FON) control group. Furthermore, microchips based on the hybrid substrates are facilely achieved, enabling micro-detection through super hydrophobic concentration. The facile fabrication and effective Raman enhancements make the Ag-islands on 3D photonic crystals promising candidates in the field of chemical sensors, Raman mapping and bioassays.

Advanced Photocatalysts Based on Reduced Nanographene Oxide-TiO2 Photonic Crystal Films.

Surface functionalization of TiO2 inverse opals by graphene oxide nanocolloids (nanoGO) presents a promising modification for the development of advanced photocatalysts that combine slow photon-assisted light harvesting, surface area, and mass transport of macroporous photonic structures with the enhanced adsorption capability, surface reactivity, and charge separation of GO nanosheets. In this work, post-thermal reduction of nanoGO–TiO2 inverse opals was investigated in order to explore the role of interfacial electron transfer vs. pollutant adsorption and improve their photocatalytic activity. Photonic band gap-engineered TiO2 inverse opals were fabricated by the coassembly technique and were functionalized by GO nanosheets and reduced under He at 200 and 500 °C. Comparative performance evaluation of the nanoGO–TiO2 films on methylene blue photodegradation under UV-VIS and visible light showed that thermal reduction at 200 °C, in synergy with slow photon effects, improved the photocatalytic reaction rate despite the loss of nanoGO and oxygen functional groups, pointing to enhanced charge separation. This was further supported by photoluminescence spectroscopy and salicylic acid UV-VIS photodegradation, where, in the absence of photonic effects, the photocatalytic activity increased, confirming that fine-tuning of interfacial coupling between TiO2 and reduced nanoGO is a key factor for the development of highly efficient photocatalytic films.

Preparation of inverse opal titanium dioxide for photocatalytic performance research

Inverse opal structure materials, with three-dimensional periodic structure and excellent optical properties, have been widely studied in many fields. In this study, visible light-driven inverse opal titanium dioxide photocatalysts were successfully fabricated via sol-gel method cooperating opal template. The surface morphology, chemical composition, crystal phase, optical absorption, optical reflectance and separation of charge carries of samples were symmetrically investigated by SEM, EDS, XRD, UV–vis DRS, UV-Raman and PL. It was found that such the structure existed electronic band gap and photonic band gap. Meanwhile, slow photon effect and larger specific surface area, reduced combination rate of photo-generated electron-hole pairs were certified. All of these properties contributed to promoting the photocatalytic redox activity of RhB degradation. Among the inverse opal TiO2 samples, IOT-610 fabricated by polystyrene microsphere opal template with the diameter of 610 nm had the best photocatalytic performance, showing 3.2 times higher than that of conventional TiO2. The results indicated that inverse opal structure photocatalyst is a preferential option for photocatalytic degradation of various environmental contaminants.

Rapidly and highly efficient degradation of tetracycline hydrochloride in wastewater by 3D IO-TiO2-CdS nanocomposite under visible light

ABSTRACT Tetracycline hydrochloride as an environmental pollutant is biologically toxic and highly difficult to degrade. To solve this problem, an efficient catalyst IO-TiO2-CdS composite with honeycomb-like three-dimensional (3D) inverse opal TiO2 (IO-TiO2) and cadmium sulphide (CdS) was synthesized and applied in the degradation of tetracycline hydrochloride in this paper. More than 99% of the tetracycline hydrochloride (30 mg/L) can be degraded by IO-TiO2-CdS (30 mg) within 20 min under visible light irradiation. Surprisingly, the naphthol rings can be opened and degraded to alkane with a minimum molecular weight of 60, which is the smallest fragment among all publications. The three-dimensional ordered macroporous (3DOM) structure of IO-TiO2 improves the utilization of light via the slow photon effect. Meanwhile, the addition of CdS enhances the degradation efficiency of tetracycline by broadening the range of absorption spectrum and improving the separation of charge carrier on the catalyst. In addition to the degradation of tetracycline hydrochloride, IO-TiO2-CdS also shows a good degradation efficiency of Rhodamine B (RhB). This work provides a promising approach to construct visible light response photocatalysts with non-noble metal for efficient degradation of wastewater pollutants.

Nickel-loaded black TiO2 with inverse opal structure for photocatalytic reduction of CO2 under visible light

The photocatalytic reduction of CO2 to high value organic substances using solar energy is significantly important to resolve both energy crisis and greenhouse effect. Thus so, Ni loaded inverse opal black TiO2 (IO-B-TiO2/Ni) were successfully prepared. Combining slow photon effect of IO material, the faster charge transfer rates caused by the loading of Ni into TiO2 with the hydrogenated disorder layer of the black TiO2 for light harvesting and charge separation, the IO-B-TiO2/Ni can be used as a stable and highly efficiency catalyst for reduction of CO2. The formation rate of CO of IO-B-TiO2/Ni is 12.1 μ·mol·g−1·h−1, which is about 10.1, 5.1 and 2.0 times as P25, IO-W-TiO2 and IO-B-TiO2, respectively.

Integrating surface plasmon resonance and slow photon effects in nanoporous anodic alumina photonic crystals for photocatalysis

This study explores the potential of gold-coated titania-functionalized nanoporous anodic alumina distributed Bragg reflectors (Au-TiO2-NAA-DBRs) as platforms to enhance photocatalytic reactions by integrating “slow photons” and surface plasmon resonance (SPR).

Fabrication of Opaline ZnO Photonic Crystal Film and Its Slow-Photon Effect on Photoreduction of Carbon Dioxide.

Monodisperse ZnO particles with adjustable size have been produced on a large scale by two-step seeding-growth polyol reactions. Through spin coating of supersaturated ZnO/diethylene glycol solution and evaporation of solvent, opaline ZnO photonic crystal (PC) film with good crystallinity and uniform photonic structures can be prepared from these ZnO particles. Compared with a disorderly stacked ZnO film, the ZnO PC film shows a higher activity in photocatalytic reduction of CO2 due to the generated slow photons at the edge of the photonic band gap and their promotion to the light absorption. When the electronic band gap of ZnO matches the red edge of the photonic band gap of ZnO PC, the enhancement factor of photocatalytic activity represented by CO evolution can be maximized to 2.64-fold in the current experiment. Compared to the traditional inverse opal photocatalysts, the opaline ZnO photocatalysts are prepared by simplified and scalable procedures, and they still possess the same enhancement in activity compared to ZnO without the photonic structure, which might be broadly used in solar energy utilization, environment protection, and many other green chemical processes in the future.

Responses to the comments of Prof. Frederic Meunier

Converting solar energy into hydrogen and hydrocarbon fuels through photocatalytic H2 production and CO2 photoreduction is a highly promising approach to address growing demand for clean and renewable energy resources. However, solar-to-fuel conversion efficiencies of current photocatalysts are not sufficient to meet commercial requirements. The narrow window of solar energy that can be used has been identified as a key reason behind such low photocatalytic reaction efficiencies. The use of photonic crystals, formed from multiple material components, has been demonstrated to be an effective way of improving light harvesting. Within these nanostructures, the slow-photon effect, a manifestation of light-propagation control, considerably enhances the interaction between light and the semiconductor components. This article reviews recent developments in the applications of photonic crystals to photocatalytic H2 production and CO2 reduction based on slow photons. These advances show great promise for improving light harvesting in solar-energy conversion technologies.

Reduced Graphene Oxide Membrane Induced Robust Structural Colors toward Personal Thermal Management

Angle-independent structural colors are prepared by membrane separation-assisted assembly (MSAA) method with modified reduced graphene oxide (rGO) as the substrate membrane. We show that the wrinkled and crumpled rGO laminates not only ensure uneven morphology of colloidal film but improve color saturation by decreasing coherent scattering. In addition, we study the influence of stopband position on thermal insulation property of the colloidal film for the first time. High absolute temperature difference of 6.9 °C is achieved comparing with control sample. And films with longer stopband positions indicate better thermal insulation performance because of inherent slow photon effect in photonic structure. This general principle of thermal insulation by colloidal films opens the way to a new generation of thermal management materials.

Hollow Nanostructures for Photocatalysis: Advantages and Challenges.

Photocatalysis for solar-driven reactions promises a bright future in addressing energy and environmental challenges. The performance of photocatalysis is highly dependent on the design of photocatalysts, which can be rationally tailored to achieve efficient light harvesting, promoted charge separation and transport, and accelerated surface reactions. Due to its unique feature, semiconductors with hollow structure offer many advantages in photocatalyst design including improved light scattering and harvesting, reduced distance for charge migration and directed charge separation, and abundant surface reactive sites of the shells. Herein, the relationship between hollow nanostructures and their photocatalytic performance are discussed. The advantages of hollow nanostructures are summarized as: 1) enhancement in the light harvesting through light scattering and slow photon effects; 2) suppression of charge recombination by reducing charge transfer distance and directing separation of charge carriers; and 3) acceleration of the surface reactions by increasing accessible surface areas for separating the redox reactions spatially. Toward the end of the review, some insights into the key challenges and perspectives of hollow structured photocatalysts are also discussed, with a good hope to shed light on further promoting the rapid progress of this dynamic research field.

Evaluation of the synergistic effect between slow photons and electron trapping on the photocatalytic properties of TiO2 photonic crystals

Titanium dioxide photonic crystals (PCs) were obtained using the sol-gel method and polystyrene (PS) microspheres as a template with two different diameters: 300 nm and 460 nm. The resulting materials were labeled as PC-300 and PC-460. In the following step, PCs were modified with silver nanoparticles (AgNPs) generated by the photoreduction of silver Ag+ ions. The obtained PCs were denoted as AgNPs/PC-300 and AgNPs/PC-460. The size of the AgNPs were 28 nm ± 2 nm for the AgNPs/PC-300 and 21 nm ± 1 nm for AgNPs/PC-460. The characteristic features of TiO2 PCs, such as electronic band gap (BG), photonic band gap (PBG) and an occurrence of slow photon effect (SPE), were determined with the use of UV–vis spectroscopy. The photocatalytic performance of the prepared PCs was defined by monitoring the photodegradation rates of Rhodamine B (RhB) measured in the presence of PC-300, PC-460, AgNPs/PC-300, AgNPs/PC-460 and non-porous TiO2 coating (NPC) as reference material.It was found that the appropriate utilization of SPE by overlapping the edge of PBG with semiconductor BG and electron trapping by the presence of AgNPs exerted a strong synergistic effect on the photocatalytic properties of AgNPs/PCs.

Blue-edge slow photons promoting visible-light hydrogen production on gradient ternary 3DOM TiO2-Au-CdS photonic crystals

The slow photon effect, a structural effect of photonic crystal photocatalyst, is very efficient in the enhancement of photocatalytic reactions. However, slow photons in powdered photonic crystal photocatalyst have rarely been discussed because they are usually randomly oriented when the photocatalytic reaction happens in solution under constant stirring. In this work, for the first time we design a gradient ternary TiO2-Au-CdS photonic crystal based on three-dimensionally ordered macroporous (3DOM) TiO2 as skeleton, Au as electron transfer medium and CdS as active material for photocatalytic H2 production under visible-light. As a result, this gradient ternary photocatalyst is favorable to simultaneously enhance light absorption, extend the light responsive region and reduce the recombination rate of the charge carriers. In particular, we found that slow photons at blue-edge exhibit much higher photocatalytic activity than that at red-edge. The photonic crystal photocatalyst with a macropore size of 250 nm exhibits the highest visible-light H2 production rate of 3.50 mmolh−1g−1 due to the slow photon energy at the blue-edge to significantly enhance the incident photons utilization. This work verifies that slow photons at the blue-edge can largely enhance light harvesting and sheds a light on designing the powdered photonic crystal photocatalyst to promote the photocatalytic H2 production via slow photon effect.

Angle dependence in slow photon photocatalysis using TiO2 inverse opals

The slow photon effect was studied by means of the photocatalytic degradation of stearic acid over TiO2 inverse opals. The comparison of the degradation rates over inverse opals with those obtained over disordered structures at different irradiation angles showed that the irradiation at the blue edge of the stopband leads to the activation of the effect, evidenced by an improvement factor of 1.8 ± 0.6 in the reaction rate for irradiation at 40°. The rigorous coupled-wave analysis (RCWA) method was employed to confirm the source of the enhancement; simulated spectra showed an enhancement in the absorption of the TiO2 matrix that composes the inverse opal at a 40° irradiation angle, owing to an appropriate position of the stopband in relation to the absorption onset of TiO2.

A bio-inspired photonic nitrocellulose array for ultrasensitive assays of single nucleic acids.

Here we report a bio-inspired photonic nitrocellulose array for ultrasensitive nucleic-acid detection. The patterned photonic nitrocellulose array is inspired by the Stenocara beetle living in the desert, which can collect water on its bumpy back surface from early morning fogs so that spontaneous generation of separated reaction droplets for loop-mediated isothermal amplification (LAMP)-based detection is enabled. Owing to the slow-photon effect of the photonic nitrocellulose, the fluorescence signal of calcein produced during the LAMP reaction can be effectively enhanced (up to 32 fold), which results in dramatically improved sensitivity for the detection of single nucleic acids in 40 min. We demonstrate that Staphylococcus aureus (SA) DNA can be quantitatively detected with a limit-of-detection of 0.60 copy per μL. The consumption of reagents and sample is also remarkably reduced owing to the highly decreased dead volume of the nitrocellulose substrate. Therefore, this bio-inspired photonic nitrocellulose array is promising for carrying out inexpensive, ultrasensitive, and high-throughput nucleic-acid detection under resource-limited settings.

Slow-Photon-Effect-Induced Photoelectrical-Conversion Efficiency Enhancement for Carbon-Quantum-Dot-Sensitized Inorganic CsPbBr3 Inverse Opal Perovskite Solar Cells.

All-inorganic cesium lead halide perovskite is suggested as a promising candidate for perovskite solar cells due to its prominent thermal stability and comparable light absorption ability. Designing textured perovskite films rather than using planar-architectural perovskites can indeed optimize the optical and photoelectrical conversion performance of perovskite photovoltaics. Herein, for the first time, this study demonstrates a rational strategy for fabricating carbon quantum dot (CQD-) sensitized all-inorganic CsPbBr3 perovskite inverse opal (IO) films via a template-assisted, spin-coating method. CsPbBr3 IO introduces slow-photon effect from tunable photonic band gaps, displaying novel optical response property visible to naked eyes, while CQD inlaid among the IO frameworks not only broadens the light absorption range but also improves the charge transfer process. Applied in the perovskite solar cells, compared with planar CsPbBr3 , slow-photon effect of CsPbBr3 IO greatly enhances the light utilization, while CQD effectively facilitates the electron-hole extraction and injection process, prolongs the carrier lifetime, jointly contributing to a double-boosted power conversion efficiency (PCE) of 8.29% and an increased incident photon-to-electron conversion efficiency of up to 76.9%. The present strategy on CsPbBr3 IO to enhance perovskite PCE can be extended to rationally design other novel optoelectronic devices.

Charge transfer induced unexpected red-shift absorption of Zn and Cu porous coordination polymers based on electron-withdrawing ligand

In the research of wide-range light-absorbing coordination polymers, to enhance intermolecular or intramolecular charge transfer (CT) and decrease the electron transition excitation energy, a dedicatedly designed novel pyridine diketopyrrolopyrrole (DPP) ligand with strong electron-withdrawing unit were introduced into the Zn, Cu and 1,4-benzenedicarboxylic acid (BDC) based coordination frameworks and porous coordination polymers DPP-Zn(BDC) and DPP-Cu(BDC) were obtained, respectively. By comparing study with physically-mixed samples DPP + Zn(BDC) and DPP + Cu(BDC), a fresh light-absorbing peak around 720 nm is observed and makes the samples exhibit a wide-range absorption in the range of 200–1400 nm and gives another experimental evidence for the research of charge transfer effect in naphthalenediimide-based metal-organic framework Zn2(NDC)2(DPNI) (J. Phys. Chem. Lett. 2013, 4, 453–458). The tremendous red-shift of absorbing onset wavelength could be ascribed to the enhanced intermolecular or intramolecular CT due to electron-withdrawing DPP ligands. At the mean time slow-photon effect is also discussed. The materials have been also characterized through powder XRD, FT-IR, SEM, XPS, solution-state spectra techniques and etc. This study underscores the importance of analyzing the extended structure for interpreting photophysical data based on the potential factors: CT, slow photon, or J-coupling. Moreover the research work might inspire the construction of light-responsive coordination polymers or metal-organic frameworks (MOFs) for charge or electron transfer.

Constructing photocatalyst from β-Bi2O3 photonic crystals for enhanced photocatalytic performance

Photonic crystals with highly ordered structure have presented a prospective application in the design of photocatalysts. Herein, we fabricated visible-light active β-Bi2O3 photonic crystals via a modified sandwich infiltration method. By using the acetylacetone-complexed metal ion precursors, pure β-Bi2O3 photonic crystals with highly ordered structure could be obtained at a calcination temperature of 400 °C. Benefited from the facilitated mass transport in the highly ordered structure, β-Bi2O3 photonic crystals exhibited higher photocatalytic activity towards organic pollutions degradation than porous β-Bi2O3 and β-Bi2O3 nanocrystals. Furthermore, the photonic band gap of β-Bi2O3 photonic crystals could be modulated to overlap its electronic band gap by changing the macropore diameter into 220 nm. Slow photon effect could be observed over the β-Bi2O3 photonic crystals with a pore diameter of 220 nm, which enhanced the electronic band gap absorption and further improved the corresponding photocatalytic activity. The enhanced activity stability of β-Bi2O3 photonic crystals could also be observed. Based on the detection of active species, the degradation mechanism over β-Bi2O3 photonic crystals was discussed. The fabrication of β-Bi2O3 photonic crystals in this study provides experimental guidance for developing photonic crystals with enhanced visible light absorption and photocatalytic activities.

Au Nanoparticles coupled Three-dimensional Macroporous BiVO4/SnO2 Inverse Opal Heterostructure For Efficient Photoelectrochemical Water Splitting

We demonstrated a strategy for coupling Au nanoparticles with ordered inverse opal heterostructure (Au-BiVO4/SnO2 IO) via a novel template-assisted, swell-to-shrink, hydrothermal method. The synergistic function of surface plasmon resonance (SPR) effect of Au nanoparticles and slow photon effect of inverse opal structure on photoelectrochemical water splitting performance of Au-BiVO4/SnO2 IO is investigated. The Au-BiVO4/SnO2 IO shows enhanced light absorption ability in visible region and suppressed recombination of photogenerated electron–hole pairs. The inverse opal structure enables light to bounce and scatter between the highly ordered tunnels, leading to efficient light harvesting. By overlapping the slow photon effect of inverse opal, the SPR effect is effectively amplified, leading to a more striking enhancement in light utilization. The Au-BiVO4/SnO2 IO displays a photocurrent density of 3.83mAcm−2 and an IPCE of 70.8% at 1.23V vs. RHE, more than 3 times higher than planar BiVO4. The improved photoelectrochemical performance is attributed to two aspects: one is the enhanced light harvesting from the coupling between the slow light and SPR effect, the other is the efficient separation of charge carriers owing to the Schottky barriers. The work provides promising strategies for designing plasmon coupled inverse opal semiconductor photoelectrodes to synergistically enhance PEC performance.

Patterned Photonic Nitrocellulose for Pseudopaper ELISA.

We report an enzyme-link immunosorbent assay (ELISA) based on patterned pseudopaper that is made of photonic nitrocellulose for highly sensitive fluorescence bioanalysis. The pseudopaper is fabricated using self-assembled monodisperse SiO2 nanoparticles that are patterned on a polypropylene substrate as template. The self-assembled nanoparticles have a close-packed hexagonal (opal) structure, so the resulting nitrocellulose has a complementary (inverse opal) photonic structure. Owing to the slow-photon effect of the photonic structure, fluorescence emission for ELISA is enhanced by up to 57-fold without increasing the assay time or complexity. As the detection signal is significantly amplified, a simple smartphone camera suffices to serve as the detector for rapid and on-site analysis. As a demonstration, human IgG is quantitatively analyzed with a detection limit of 3.8 fg/mL, which is lower than that of conventional ELISA and paper-based ELISA. The consumption of sample and reagent is also reduced by 33 times compared with conventional ELISA. Therefore, the pseudopaper ELISA based on patterned photonic nitrocellulose is promising for sensitive, high-throughput bioanalysis.

Synergetic Enhancement of Light Harvesting and Charge Separation over Surface-Disorder-Engineered TiO2 Photonic Crystals

Summary Solar light harvesting and charge separation are both critical to the solar-to-energy conversion in photocatalysis, but it is difficult to simultaneously achieve both in a single-component material. This paper describes the design and synthesis of dual-functional surface-disorder-engineered titanium dioxide photonic crystals (TiO 2 PCs) for efficient solar light harvesting and charge separation in photocatalytic hydrogen evolution. The slow photon effect of TiO 2 PCs enhances the photon-matter interaction to increase light harvesting, and the disorder-engineered surface layer can form band tail states and trap centers to promote the separation and inhibit the recombination of charge carriers. The synergetic enhancement of light harvesting and charge separation in this single-component material leads to a high performance toward photocatalytic hydrogen evolution. This approach provides a promising strategy for designing dual-functional materials with a high solar-to-energy conversion efficiency for various photocatalytic processes.